關(guān)于阿里巴巴TransmittableThreadLocal使用解讀

更新時(shí)間：2025年02月14日 15:41:28 作者：林犀居士

文章主要介紹了三種ThreadLocal的使用：ThreadLocal、InheritableThreadLocal和TransmittableThreadLocal,ThreadLocal和InheritableThreadLocal在單線程和部分情況下可以正常工作,但TransmittableThreadLocal在處理線程池時(shí)表現(xiàn)更佳

前言

ThreadLocal在上下文的數(shù)據(jù)傳輸上非常的方便和簡潔。

工業(yè)實(shí)踐中，比較常用的有三個(gè)，ThreadLocal、InheritableThreadLocal、TransmittableThreadLocal，那么他們?nèi)齻€(gè)之間有什么區(qū)別呢？

常見的三種ThreadLocal比較

	ThreadLocal	InheritableThreadLocal	TransmittableThreadLocal
來源	jdk	jdk	阿里開源
單線程數(shù)據(jù)傳輸	支持	支持	支持
new線程數(shù)據(jù)傳輸	不支持	支持	支持
線程池?cái)?shù)據(jù)傳輸	不支持	部分支持【簡單場景】	支持

針對(duì)線程池的數(shù)據(jù)傳輸，InheritableThreadLocal僅僅能在一些簡單場景下做到，下面就用一個(gè)案例來說明

先看下線程工廠的定義

package com.tml.mouseDemo.core.threadLocalDemo;

import java.util.concurrent.ThreadFactory;
import java.util.concurrent.atomic.AtomicInteger;

public class SimpleThreadFactory implements ThreadFactory {

    private static AtomicInteger atomicInteger = new AtomicInteger(1);
    @Override
    public Thread newThread(Runnable r) {

        Thread t = new Thread(r);
        t.setName("tml-"+atomicInteger.getAndIncrement());
        return t;
    }
}

InheritableThreadLocal部分支持的案例

package com.tml.mouseDemo.core.threadLocalDemo;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ThreadLocalDemo1 {

    private static ThreadLocal<String> threadLocal = new InheritableThreadLocal<>();

    private static ExecutorService service = Executors.newFixedThreadPool(2, new SimpleThreadFactory());


    public static void main(String[] args) throws InterruptedException {


        threadLocal.set("hello main");
        for (int i = 0; i < 2; i++) {
            service.execute(() -> {
                String s = threadLocal.get();
                ThreadUtils.printLog("get data " + s);

            });
        }

        //修改threadLocal中的值
        threadLocal.set("hello world");
        Thread.sleep(2000);
        for (int i = 0; i < 2; i++) {

            service.execute(() -> {
                String s = threadLocal.get();
                ThreadUtils.printLog("get data " + s);

            });
        }


        ThreadUtils.printLog("get data " + threadLocal.get());

        service.shutdown();

    }
}

運(yùn)行結(jié)果如下

2025-01-10 19:41:50 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 19:41:50 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 19:41:52 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 19:41:52 | INFO | main | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world
2025-01-10 19:41:52 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main

從運(yùn)行結(jié)果來看，前面的兩次循環(huán)提交的任務(wù)，在子線程中確實(shí)是能正常的獲取主線程設(shè)置的變量，即hello main，但是緊接著，我修改了主線程上綁定的變量為hello world，然后繼續(xù)循環(huán)兩次提交兩個(gè)任務(wù)，這個(gè)時(shí)候子線程中獲取的線程變量依然是hello main，這明顯是與是期望不一致的。

從這個(gè)層面來講，InheritableThreadLocal確實(shí)在線程池的層面支持不夠友好，可以說僅支持部分簡單場景。

根本原因就死線程池的池化機(jī)制，從上面的運(yùn)行日志上也可以看出，提交了4個(gè)任務(wù)執(zhí)行的線程依然是兩個(gè)。線程池中的線程是復(fù)用的，InheritableThreadLocal是在創(chuàng)建子線程的時(shí)候，會(huì)將主線程上綁定的數(shù)據(jù)拷貝過來，如果我不創(chuàng)建新的線程，但是主線程上綁定的數(shù)據(jù)改變了呢？那我依然還是讀取到之前拷貝的數(shù)據(jù)。

這個(gè)就是InheritableThreadLocal的短板。針對(duì)這個(gè)問題，阿里開源的TransmittableThreadLocal就能順利絲滑的解決這個(gè)問題。

TransmittableThreadLocal實(shí)踐

maven依賴

<dependency>
     <groupId>com.alibaba</groupId>
    <artifactId>transmittable-thread-local</artifactId>
     <version>2.12.4</version>
</dependency>

裝飾Runnable任務(wù)

直接看代碼

package com.tml.mouseDemo.core.threadLocalDemo;

import com.alibaba.ttl.TransmittableThreadLocal;
import com.alibaba.ttl.TtlRunnable;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ThreadLocalDemo1 {

    private static ThreadLocal<String> threadLocal = new TransmittableThreadLocal<>();

    private static ExecutorService service = Executors.newFixedThreadPool(2, new SimpleThreadFactory());


    public static void main(String[] args) throws InterruptedException {


        threadLocal.set("hello main");
        for (int i = 0; i < 2; i++) {
            service.execute(TtlRunnable.get(() -> {
                String s = threadLocal.get();
                ThreadUtils.printLog("get data " + s);

            }));
        }

        //修改threadLocal中的值
        threadLocal.set("hello world");
        Thread.sleep(2000);
        for (int i = 0; i < 2; i++) {

            service.execute(TtlRunnable.get(() -> {
                String s = threadLocal.get();
                ThreadUtils.printLog("get data " + s);

            }));
        }


        ThreadUtils.printLog("get data " + threadLocal.get());

        service.shutdown();

    }
}

運(yùn)行結(jié)果如下：

2025-01-10 19:57:03 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 19:57:03 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 19:57:05 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world
2025-01-10 19:57:05 | INFO | main | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world
2025-01-10 19:57:05 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world

與第一個(gè)案例的差異點(diǎn)在于，使用了

public static TtlRunnable get(@Nullable Runnable runnable) {
    return get(runnable, false, false);
}

來增強(qiáng)了了Runnable任務(wù)，執(zhí)行的結(jié)果也是符合預(yù)期。

裝飾線程池

直接看代碼

package com.tml.mouseDemo.core.threadLocalDemo;

import com.alibaba.ttl.TransmittableThreadLocal;
import com.alibaba.ttl.TtlRunnable;
import com.alibaba.ttl.threadpool.TtlExecutors;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ThreadLocalDemo1 {

    private static ThreadLocal<String> threadLocal = new TransmittableThreadLocal<>();

    private static ExecutorService service = Executors.newFixedThreadPool(2, new SimpleThreadFactory());

    private static ExecutorService ttlExecutorService = TtlExecutors.getTtlExecutorService(service);



    public static void main(String[] args) throws InterruptedException {



        threadLocal.set("hello main");
        for (int i = 0; i < 2; i++) {
            ttlExecutorService.execute(() -> {
                String s = threadLocal.get();
                ThreadUtils.printLog("get data " + s);

            });
        }

        //修改threadLocal中的值
        threadLocal.set("hello world");
        Thread.sleep(2000);
        for (int i = 0; i < 2; i++) {

            ttlExecutorService.execute(() -> {
                String s = threadLocal.get();
                ThreadUtils.printLog("get data " + s);

            });
        }


        ThreadUtils.printLog("get data " + threadLocal.get());

        service.shutdown();

    }
}

運(yùn)行結(jié)果如下

2025-01-10 20:05:05 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 20:05:05 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 20:05:07 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world
2025-01-10 20:05:07 | INFO | main | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world
2025-01-10 20:05:07 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world

與上一個(gè)案例的差異點(diǎn)在于，這里沒有包裝Runnable任務(wù)，而是包裝了線程池，使用了

public static ExecutorService getTtlExecutorService(@Nullable ExecutorService executorService) {
    if (TtlAgent.isTtlAgentLoaded() || executorService == null || executorService instanceof TtlEnhanced) {
        return executorService;
    }
    return new ExecutorServiceTtlWrapper(executorService, true);
}

包裝了ExecutorService，執(zhí)行結(jié)果也是符合預(yù)期

使用java Agent無侵入增強(qiáng)線程池

直接看代碼

package com.tml.mouseDemo.core.threadLocalDemo;

import com.alibaba.ttl.TransmittableThreadLocal;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class ThreadLocalDemo1 {

    private static ThreadLocal<String> threadLocal = new TransmittableThreadLocal<>();

    private static ExecutorService service = Executors.newFixedThreadPool(2, new SimpleThreadFactory());

    public static void main(String[] args) throws InterruptedException {



        threadLocal.set("hello main");
        for (int i = 0; i < 2; i++) {
            service.execute(() -> {
                String s = threadLocal.get();
                ThreadUtils.printLog("get data " + s);

            });
        }

        //修改threadLocal中的值
        threadLocal.set("hello world");
        Thread.sleep(2000);
        for (int i = 0; i < 2; i++) {

            service.execute(() -> {
                String s = threadLocal.get();
                ThreadUtils.printLog("get data " + s);

            });
        }


        ThreadUtils.printLog("get data " + threadLocal.get());

        service.shutdown();

    }
}

項(xiàng)目運(yùn)行的時(shí)候，需要添加額外的jvm啟動(dòng)參數(shù)，如下

運(yùn)行結(jié)果如下，也是符合預(yù)期

2025-01-10 20:11:59 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 20:11:59 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello main
2025-01-10 20:12:01 | INFO | tml-2 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world
2025-01-10 20:12:01 | INFO | main | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world
2025-01-10 20:12:01 | INFO | tml-1 | com.tml.mouseDemo.core.threadLocalDemo.ThreadUtils | get data hello world